The present invention relates generally to pumps and hydraulically-actuated systems used with internal combustion engines, and more particularly to axial hydraulic pumps with wobble plates.
Hydraulic pumps that utilize wobble plates to drive reciprocating pistons are susceptible to wear. The wobble plate is usually the driveplate with a tilted pumping surface that pushes against the pump""s pistons. As the driveplate rotates each piston is pushed away from the driveplate as the thickness of the driveplate beneath it becomes greater with the rotation, causing the piston to compress. The hydraulic pressure within the piston increases as the volume within the piston decreases. This high pressure hydraulic fluid is generally the output product of the hydraulic pump. As rotation continues and the thickness of the driveplate beneath the piston lessens, the higher hydraulic pressure within the piston allows it to expand again and refill itself with lower pressure hydraulic fluid.
There is generally friction between the driveplate and the piston as the driveplate rotates. This can cause wear to the piston and driveplate surfaces. Additionally, there is generally friction and wear against other surfaces that the rotating driveplate comes in contact with, as well.
Of course, the driveplate and whatever holds it must also be capable of bearing the loads caused by pushing against the compressing pistons. These loads may be axial (i.e., parallel to the drive shaft axis and/or perpendicular to the plaintiff rotation of the driveplate) or radial (i.e., perpendicular to the drive shaft axis), or some combination thereof.
A displacement pump 1 according to one aspect of the invention has a rotatable drive shaft 9 and at least one piston 20 containing a piston cavity 62, and a piston shoe 34 flexibly connected with the piston 20. The piston shoe 34 comprises a shoe passage 60 fluidly connected with the piston cavity 62. The displacement pump also has a hydrostatic thrust bearing plate 40 comprising at least one thrust pad 42, and a driveplate 12 connected with the drive shaft 9 and disposed between the piston shoe 34 and the thrust pad 42. The driveplate 12 comprises a bearing surface 46 proximate to the thrust pad 42, a pumping surface 38 proximate to the piston shoe 34, and at least one communication port 48 fluidly connecting the bearing surface 46 with the pumping surface 38. The driveplate 12 is rotatable to a position in which the piston cavity 62 is fluidly connected with the thrust pad 42 via the shoe passage 60 and the communication port.